1. Field of the Invention
The invention relates generally to seismic energy detection devices and, more particularly, but not by way of limitation, it relates to a high sensitivity detection apparatus that utilizes laser beam energy for detection of the velocity of earth surface movement.
2. Description of the Prior Art
To the knowledge of this source the seismic art has not yet utilized light energy techniques for isolation of earth surface movement as caused by seismic energy vibrations. High frequency light energy, specifically the laser and related devices, has been utilized for various velocimetric purposes where the particular application lends itself to the surrounding physical conditions and exigencies of the particular application. For example, Doppler frequency measurement techniques are well-known in a number of radar-type applications as well as in certain measurement methods for fluid streams, turbulent layers in fluids and other forms of small amplitude vibration that occur in the various phases of non-destructive testing. In all of the applications known to the present Applicant, such measurement schemes take the form of beam transmission and transition patterns wherein the transmitted beam traverses a different space or path than the reflected beam or beams prior to detection and readout such that variations in the traversed matter will greatly affect the readout results as it relates to frequency and the attendant distance variations. That is, variations as to the travel paths of the high frequency light energy, e.g. as regards differences in the physical paths through air, constitution of the air and heat effects, will more often than not result in a total degredation of the finite measurement qualitites of the energy. This would be especially true as regards the minute variations to be encountered relative to seismic energy disturbances.
The closest prior art encountered today is believed to be the U.S. Pat. No. 3,409,369 in the name of Bickel, a laser radar application wherein the source-target-detector path is nearly along the same traverse; however, this application utilizes a still further differential frequency energy input in order to ascertain the velocity of moving objects under detection surveillance.